Can bread mold in one day?

Yes, bread can mold in one day if the conditions are right. Mold spores are always present in the air, and they need three things to grow: moisture, warmth, and food. Bread provides all of these things. If bread is left out in a warm, humid environment, the mold spores will start to grow and multiply. Within 24 hours, you could see visible mold growth on the bread.